1. Field of the Invention
The present invention relates to an analog electronic timepiece which includes a measuring function of geomagnetic field.
2. Description of Related Art
Conventionally, there have been analog electronic timepieces which individually drive a plurality of stepping motors and can independently move their corresponding hands. Such analog electronic timepieces can rapidly move the hands in a case where a plurality of hands are used for a purpose other than time display and in a case where positions of hands according to time display are largely moved.
Such analog electronic timepieces include multifunctional electronic timepieces which have a function of measuring various physical quantities such as the acceleration, magnetic field (geomagnetic field), atmosphere and temperature and displaying information according to the physical quantities. Some of the multifunctional electronic timepieces are provided with one or a plurality of functional hand(s) for displaying the information in addition to an hour hand, a minute hand and a secondhand for the time display. Also, even in a case where the functional hand is not provided, the display according to the function may be performed by operating only one or two hand(s) as in a case where compass display or direction display is performed on the basis of measurement of geomagnetic field. In these cases, the time display can be simultaneously performed in parallel by a hand other than the functional hand or a hand which is not used for functional display.
However, in analog electronic timepieces, a magnetic field is generated according to rotation of a rotor when a stepping motor is driven. In addition, the stepping motor is easily magnetized to produce an offset magnetic field, and thus the offset magnetic field changes during the rotation of the rotor. Especially, the magnetic field measured at a compact wristwatch is easily influenced by the offset magnetic field. Thus, conventionally, there has been known an electronic analog timepiece which detects an operation state of a stepping motor and detects a direction only in a state where the stepping motor is stopped, and such electronic analog timepiece is described in Japanese Patent Laid-Open Publication No. H5-312573, for example. Also, Japanese Patent No. 3596201 describes a technique in which the direction is detected with the same period as the period of hand operation according to the time display and at a phase different from the hand operation.
However, in a case where magnetic field measurement and display of the magnetic field and direction are performed along with time display by using hands of the analog electronic timepiece, the rotation angle of hand per rotation changes according to the amount of change in the measured magnetic field. Since the rotation frequency (rotation speed) of hand is determined according to conditions such as performance of stepping motor and gear, time required for moving hands also changes according to the rotation angle per rotation. Accordingly, in a case where a desired time resolution of magnetic field measurement is high compared to the rotation speed of hand, there is a possibility that the hand operation for displaying magnetic field and direction and the magnetic field measurement thereafter are performed at a timing which overlaps an operation timing of the hands according to time display. That is, by the time which is required for the magnetic field measurement and the hand operation according to the magnetic field display changing irregularly, the hands used for the time display cannot be operated at the accurate timing and, and the time interval of magnetic field measurement becomes inappropriately large, which disturbs comfortable use of a user.
The present invention relates to an analog electronic timepiece which can perform, in parallel, information display according to time counting operation and information display according to magnetic field measurement which a user can comfortably obtain.